SE521135C2 - A communication network and a fault management method in such a network - Google Patents

Abstract

A communications network comprising at least two nodes is disclosed. The network has two communication paths that carry traffic in opposite directions and work as a bi-directional bus. The network has a first inactive segment that carries no traffic and is arranged to allow the first inactive segment to be made active and another segment to be made inactive, especially in the case of fault in the other segment. The activation and inactivation logically "move" the first inactive segment. Additional protection paths are provided between the nodes.

Description

25 30 JJ (J '\ 521 155š * ÄIfi% ¥ -Hïßfï 2 with optical ring network architectures, with circulating signals and noise.

In the FlexBusTM architecture, a section or segment of the fiber ring is always passive or inactive by means of optical switches or amplifiers. This intentionally introduced interruption effectively eliminates all problems associated with circulating signals and thus allows smaller circuitry in the case of lower performance components to be used. a real fault of a section or link, which is intentionally made inactive, is logically "moved" logically from its previous position to the wrong position by making the inactive segment active and the incorrect segment inactive, which is also called "bus flexing", and thereby restoring traffic.

Various developments of FlexBusTM can be found, for example, in WO 96/31025 and WO 96/24998.

DESCRIPTION OF THE INVENTION A problem with FlexBusTM and many other error handling algorithms in communication networks is that they can only handle one error at a time. In FlexBusTM, this is due to the fact that when a deactivated segment includes a fault, it cannot be logically moved as described above before the fault is repaired, due to the fact that otherwise the bus would not work.

An object of the invention is to solve this problem by using protective links in parallel with the ordinary links. If an error occurs, the deactivated segment will be logically moved to the error as usual. A bypass is performed over the protection links in parallel with the first deactivated segment and a second deactivated segment is created instead of the now deactivated deactivated faulty segment.

Since the second deactivated segment does not include an error, it is possible to logically move it in the event of the occurrence of a second error. When the second deactivated segment has been logically moved to the second error l0 l5 20 25 30 (JJ (Jl 521 13àš¶ ¥ 1ï “® 3), a third deactivated segment will, in the same way, be created in parallel with the second deactivated segment. The third deactivated segment is thus possible to logically move in the case of a third error, etc. This can of course not be extended forever, it depends on what the network of protection links looks like and it may happen that the new error occurs on a place where it is not remedial.

However, it is rare for more than one or two errors to occur at the same time, so in practice it will not be a problem.

The advantages of this are that a simple and inexpensive error handling procedure is achieved, which can take care of many common errors.

If the links are also physically parallel, an interruption in a protection link is likely to occur simultaneously as an interruption in an ordinary link. This problem is solved in an embodiment of the invention in that multidirectional cross points are used to connect different protection links in a more flexible way, forming a kind of network.

The advantages of this embodiment are that it is safe, that already existing links can be used as protection links and that a more flexible bus reconfiguration is possible in the case when a large part of the ordinary ring is incorrect.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by means of non-limiting embodiments with reference to the accompanying drawings, in which: Figure 1 shows a general schematic view of a WDM type optical fiber network using the flexible bus architecture Figure 2 shows a block diagram of an addition and removal node according to the prior art with a simple configuration and intended for use in the network according to Figure 1, Figure 3a shows a general schematic view of a network according to the invention, with a working deactivated segment S1, 10 15 20 25 30 35 521 135 4 - figure 3b shows the network in figure 3a with a non-working deactivated segment S1 and a working deactivated segment S2, figure 3c shows the network in figure 3a, b with a non-working deactivated segment S1, a non-working deactivated segment S2 and a working deactivated segment S3, - figure 3d shows the network in figure 3a, b with a non-working deactivated segment S1 and a working deactivated segment S2, Figure 4 shows a block diagram of a multidirectional crossing point. Figures 5a and b show a block diagram of an addition and removal node according to a first embodiment, Figure 6 shows a block diagram of an addition and removal node according to a second embodiment, Figure 7 shows a block diagram of an addition and removal node. - removal node according to a third embodiment, - figure 8 shows a block diagram of an addition and removal node according to a fourth embodiment, - figure 9 shows a block diagram of an addition and removal node according to a fifth embodiment, - figure 10 shows a block diagram of an addition and removal node according to a sixth embodiment, Figure 11 shows a block diagram of an addition and removal node according to a seventh embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS The known FlexBusTM concept will be described in more detail below. It will be appreciated that although only wavelength division multiplexing (WDM) will be described, the error handling method also works with other multiplexing techniques, using nodes with an xnote-like design.

A flexible base bus structure for WDM communication and optical fibers is illustrated in Figure 1. A plurality of optical addition and removal nodes N are connected to each other by links 1 to form a network or bus comprising 10 U 20 UT 521 135 5 a physical ring structure which as a basic element has a pair of optical fibers 2, 3 connected to form two parallel fiber rings.

Each fiber ring transmits light which propagates in a specific direction, for the two whereby the propagation directions the rings are opposite each other. In one of the fiber rings, light always propagates in the counterclockwise direction, in the embodiment according to Figure 1 it is the inner ring 2, this direction hereinafter referred to as the east direction. In the other 3 of the rings with the pair of fiber rings, light always propagates in the opposite direction, ie in the clockwise direction, as shown in Figure 1, this direction being called the western direction. These directions are obtained as related to a considered node N of the network. In order to understand the concepts of “east” and “west” correctly, it can be helpful to imagine the ring as the equator.

A node N in the bus structure is thus physically connected to two adjacent nodes. The connections for a considered node N comprise a physical west link lw comprising a west line cable 4w and a physical east link le comprising an east line cable 4e, the other end of each link lw, le being connected to an adjacent node.

Each part 4w, 4e of the lead cables comprises a pair of optical fibers 2w, 3w and 2e, 3e, respectively. In a 2w, 2e of the fibers of a fiber pair in a link 4w, 4e light always propagates in one direction, in the counterclockwise direction as shown in figure 1. In the other 3w, 3e of the fibers of the fiber pair in a link 4w, 4e light always propagates in the opposite direction, in the clockwise direction, as shown in Figure 1.

A node N may further comprise receiver 5 and transmitter 6 for converting optical signals into electrical signals and vice versa, the electrical signals being transmitted to or received from other devices, links or networks, not shown.

A segment of the ring structure is always deactivated, compare link 7 in figure 1, so that at least no light-transmitting traffic to be transmitted in the network can pass through, in any direction. Pure signaling can be allowed to pass it 10 15 20 25 30 DJ U! 521 1ssï *.} F 6 activated the segment, e.g. by using a special signaling channel that bypasses the node in a special path. In a way, the activated segment can thus also be considered as part of the bus.

The deactivated segment prevents light signals and ASE noise from circulating with the ring structure in several turns, whereby ASE noise is amplified spontaneous emission, in particular from in-line optical amplifiers which are usually included in the nodes N.

When there is an error in a link between adjacent nodes N, the network can be reconfigured so that this link / segment will then be the deactivated one, while the previously deactivated segment 7 is now deactivated and functions as the other active links 1 in the ring structure permitting traffic in the two opposite directions. In this application, this will be referred to as “moving” a deactivated segment, whereby “moving” in this context means “logically moving”. A flag is placed somewhere indicating that the present deactivated segment contains an error and thus cannot be "moved".

A basic structure of a node N in the flexible basic bus structure of Figure 1 is shown in the block diagram of Figure 2. The optical WDM traffic comprises a plurality of WDM channels of fixed, separate wavelengths, each channel comprising one occupying a wavelength band around the wavelength of the channel. enters the node from the left or west and from the right or east directions of the fibers 2w and 3e, respectively.

The incoming signals can be amplified in optional optical amplifiers Pw and Pe, respectively. The incoming light is then divided into drain switches llw, lle. These couplers are optical power dividers which supply part of the total power of the light propagating in one direction in the bus, via an optical combining coupler or power combiner 12, adding the deflected power parts from each direction to each other, to a bank 13 with filter, which can also be called an optical demultiplexer, with one or more band-blocking filters for wavelengths used in the transmission in the network. The filter bank 13 thus filters out channels, each channel transmitting information in a certain wavelength band which is then forwarded to optoelectric receiver 5, an optical receiver being arranged for each receiver channel.

The remaining part of the light effect divided into the drain switches llw, lle is passed on via the node N, via optional band-blocking filters l7e, l7w and is mixed in the addition switches l4e, l4w with new traffic to be added in the node. This new traffic is obtained from electro-optical transmitters 6, where each transmitter transmits optical signals with a wavelength band or a channel separate from that of the other transmitters. The output signals from the transmitters 6 are added to each other in an optical combining coupler or optical multiplexer 15. The resulting signal is divided in a dividing coupler 16 into two parts with equal power, each of the two parts being transmitted to one of the adding couplers 14e, 14w.

The light signals obtained from the addition switches 14e, 14w for each direction are fed to the fibers 3w, 2e, which are included in the links connected to the node and transmit light emanating from the node, via optional optical booster amplifiers Be, Bw.

The west side or east side amplifiers Pw, Bw or Pe, Be can respectively be used to deactivate the respective links or segments connecting the node to the two adjacent nodes in the case where this link is to be the deactivated link, as is the case with a fault in this link, which can be caused, for example, by one of the fibers of the pair of links being interrupted or by one of the optical amplifiers connected to this link being faulty.

Most of the bus structure and node construction of Figures 1, 2 are described in the above-cited article by B.S.

Johansson et al. and in the cited US 08 / 421,734.

Figure 3a shows according to the invention a communication patent application network with, as an example, eight nodes N1-N8 connected in a ring such as a FlexBus® network as described above. Somewhere a disabled segment S1 is located. Extra bi-directional links L1-L11 for protection are connected between the different nodes N1-N8, via multi-directional crossing points C1-C3 or directly between the nodes. If an error occurs in the ordinary communication network, traffic is instead directed via one or more of the protection links L1-Lll so that the error is bypassed.

The connections between the nodes N1-N8 can look different, as can be seen in Figure 3a. The important thing is that there is an extra way to get from one node to another node, without using the ordinary links.

Of course, it is possible to have a bidirectional spare ring parallel to the ordinary ring, as well as the ninth protection link L9 between the fifth and sixth nodes N5, N6.

However, if you inadvertently cut the ordinary ring, you will probably also cut the spare ring. Using multi-directional cross points will not only make it safer, but also allow existing links to be used and also allow a more flexible bus reconfiguration in the event that a large part of the ordinary ring is incorrect. 3a a little closer. For example, if a first error F1 occurs between the Let's study communication network in Figure first node N1 and the second node N2, the deactivated segment S1, regardless of where it is located from the beginning, will move to the incorrect part of the communication network, ie to the link between the first node N1 and the second node N2, compare Figure 3b.

A flag will be set, indicating that the deactivated segment S1 includes a fault and thus cannot be moved until the fault has been repaired. The bus will work, but if another fault should occur, the bus will no longer work, as the deactivated segment would not be moved if there was a fault in the link.

A "non-working" and non-movable deactivated segment S1 comprising a fault is thus obtained.

This problem is solved by the invention in that when a fault has occurred, a connection is created over the protective links which bypass the non-working deactivated segment S1. An extra “working” and movably deactivated segment S2 10 15 is thus created between the first node N1 and the second node N2 using the links L1 and L2 via the first cross point C1. The non-working deactivated segment S1 is disconnected from the bus and bypassed by the working deactivated segment S2, which instead forms part of the bus.

Of course, it is not strictly necessary to place the new working deactivated segment S2 exactly between the same two nodes N1, N2 as the old non-working deactivated segment S1 as shown in Figure 3b. It is possible to bypass the non-working deactivated segment S1 with a standard active link and place the new working deactivated segment S2 somewhere else on the bus, for example between the sixth N6 and the seventh N7 node.

When the fault is repaired, the non-working deactivated segment S1 is reset and functions again and is part of the bus. The protection paths and the second deactivated segment S2 are no longer used, and the situation is again the same according to Figure 3a, but with the deactivated segment S1 between the first and second nodes N1, N2.

Now it may happen that a second error F2 occurs before the first error F1 is repaired, for example between the fourth. In this case, the working deactivated segment S2 is moved to the node N4 and the fifth node N5, cf. Figure 3c. the faulty part of the bus and becomes non-working and no longer part of the bus. A new working deactivated segment S3 is created via the fifth L5 and sixth L6 links and the second cross point C2, thus bypassing the now non-working deactivated segment S2.

It may instead happen that the second error F2 occurs in the link closest to the link with the first error F1, i.e. between the second node N2 and the third node N3, cf. Figure 3e. In this case, an alternative may be to bypass both the first error F1 and the second error F2 at the same time if the node N2 between the two errors can be dispensed with. This is done by rearranging the operating deactivated segment S2, so as to instead comprise the protection links L1 and L3.

The construction of a multidirectional crosspoint is simple, compare Figure 4 for an example with an option to connect four external bidirectional links. preamplifier P1, P2, P3, P4, four booster amplifiers B1, B2, B3, B4, four power dividers 21, 22, 23, 24 and four power combiners 25, 26, 27, 28. On each incoming external link There are four optional there is a preamplifier P1, P2, P3, P4 connected to a power divider 21, 22, 23, 24 connected by three of the power combiners 25, 26, 27, 28. Each power combiner 25, 26, 27, 28 is in turn connected to a booster amplifier B1, B2, B3, B4.

This arrangement allows connection with optional two external bidirectional links, by simply activating the preamplifiers P1, P2, P3, P4 and the booster amplifiers B1, B2, B3, B4 on the two external links to be connected and by deactivating the other amplifiers.

To determine which amplifiers are to be activated and which are not to be activated, for example, a separate signaling channel can be used, which does not transmit any traffic, but only information regarding the status of the network, instructions for flexing and connecting protection links and the like.

If the network with protection links is not too complicated, the instructions for connecting the protection links can also be simple. For example, if the fault is on the west side of the node, as for the first node N1 in Figure 3b, the instructions in this case may be "turn left until the next node is reached", which in this case would be the second node N2. from the second node N2 to the first node N1 would then simultaneously be “turn right until the next node is reached.” The connections at the multidirectional cross points, in this case only one, will be set up accordingly.

A node in a network using the invention can look in many ways. Some of them will be described below, all of which more or less use the WDM node in Figure 2 as a basis. The same reference numerals will be used for corresponding properties. It is possible to construct new nodes by combining characteristics from different figures. Nodes in FDM and TDM networks can of course also be modified in a corresponding way. An embodiment of a node is shown in Figure 5a, which is rearranged in the equivalent Figure 5b for clarity only. In addition to the two standard optional preamplifiers Pe, Pw and the two booster amplifiers Be, Bw, there is a third optional preamplifier Pp and a third booster amplifier Bp for connection to a protection link. There are also transmitters 6 with multiplexers 15, receivers 5 with demultiplexers 13, power dividers lle, llw, llp, 16, 18p, l8e, l8w, power combiners 12, l4p, l4e, 17e, 17w.

Each preamplifier Pp, Pw, Pe is connected to one of the first three power parts 11p, llw, lle. Each first power 14w and three optional blocking filters 17p, dividers 11p, 11w, 11e are in turn connected to, on the one hand, the demultiplexers 13 via a power combiner 12, and on the other hand the three other power parts l8p, l8e, 18w, either di directly or via one of the optional blocking filters 17p, 17e, 17w.

Each other power divider 18p, l8e, 18w is connected to two of the power combiners l4p, l4e, 14w. Each power combiner 14p, 14e, 14w is thus connected to two of the other power parts 18p, 18e, 18w, but also to one of the booster amplifiers Bp, Be, Bw and to a power divider 16 connected to the multiplexers 15.

The connections are thus made to create a connection between east and west, between east and the protective link or between west and the protective link.

Of course, it would also be possible to have two protection links connected to the node; one for the east direction and one for the west direction, and ll.

The invention can also be used in more complicated terms comparing the upper parts of Figures 10d. In the following description, Figures 6, 8 and 10 show nodes that are useful for all traffic cases; while Figures 7, 9 and 11 show nodes for use in systems reusing wavelengths in combination in a situation where all traffic channels are between adjacent nodes. They are all drawn in a rearranged manner as in Figure 5b for clarity only.

The procedure for reusing wavelengths is beyond the scope of this application and will only be described briefly. instead to the Swedish applications SE9802070-4 and SE980207l-2.

A wavelength channel is said to be terminated in a node if the Interested reader is referred is received in the node, ie if there is a receiver 5 for this channel in the node. A wavelength channel is said to be reused if it is used for transmission from a node, ie if there is a transmitter 6 for this wavelength in the node, and the same wavelength is simultaneously used to transmit information in the same direction with another node without overlapping the transmission paths. Termination or reuse of wavelengths can be achieved by using blocking filters in lines l7e, l7w, l7pe, l7pw.

Each of the blocking filters l7e, l7w, l7pe, l7pw in the considered node blocks only the respective wavelengths which are terminated in the node for each direction. All wavelengths that do not end in the node only pass through the node in the east or west direction in a substantially unaffected manner.

In Figure 6, each receiver Se, 5w is connected to a switch 37e, 37w, which selects whether the wavelength of the receiver is to be received from the west preamplifier Pw, via west multiplexers 13w or from the east preamplifier Pe, via the east demultiplexers 13e. Correspondingly, each transmitter 6e, 6w is connected to a switch 38e, 38w, which selects whether the wavelength of the transmitter is to be transmitted to the west booster amplifier Bw, via the west multiplexers l5w or the east booster amplifier Be, via east multiplexers l5e.

In this case, the optional protection preamplifier Pp and the protection booster amplifier Bp are each connected to a switch 31 and 32, respectively. These switches 31, 32 serve the purpose of selecting east or west wavelengths. In order to achieve this, the two outputs of the switch 31 of the protection preamplifier Pp are each connected to a power combiner 33w, 33e followed by a power divider 34w, 34e. connected to the output of a preamplifier Pw, Pe, that each power divider 34w, band blocking filter l7e, Each power combiner 33w, 33e is also below 34e is connected to a l7w and to one of the demultiplexers l3w, l3e.

Thus, if the link east of the node is non-operative, the switch 31 of the protection preamplifier Pp is placed in its “east position” and the wavelengths coming from the east direction are received via the protection link.

Similarly, the two inputs of the switch 32 of the protection booster amplifier Bp are each connected to a power divider 36w, 36e preceded by a power divider 35w, 35e. Each power divider 36w, 36e is also connected to the input of a booster amplifier Bw, Be, while each power combiner 34w, 34e is connected to one of the band blocking filters l7e, l5w, l5e.

Thus, if the link east of the node is non-operative, and to one of the multiplexers the switch 32 of the protection booster amplifier Bp is placed in its "east position" and the east wavelengths are transmitted over the protection link.

Figure 7 is very similar to Figure 6. One difference is that the receivers 5e, 5w are connected directly to the demultiplexers 133, 133 and that the switches 41e, 41w are instead connected between the demultiplexers 133, 133 and the power parts 34w, 34e. In a corresponding manner, the transmitters 6e, 6w are connected directly to the mul- 42w are instead l5w and the power parts the tiplexors l5e, l5w and the switches 42e, connected to the pin multiplexers l5e, 35w, 35e.

Figure 8 is also very similar to Figure 6. In this case, however, there are two booster amplifiers Bpw, Bpe, instead of a preamplifier / protection preamplifier Ppw, Ppe and two booster amplifiers with a switch.

Figure 9 is in turn similar to Figure 7, except that there are two protection preamplifiers Ppw, Ppe and two booster amplifiers Bpw, Bpe, instead of a preamplifier / booster amplifier with a switch.

Figure 10 is a combination of Figure 8 and Figure 5b.

Each preamplifier Ppw, Ppe, Pw, Pe is connected to the demultiplexers 133, 133, the switches 37e, 37w and the receivers 5e, 5w as shown in Figure 8, via a first power divider 5lpw, two power combiners 54e, 54w. The first power parts 5lpw, 5lpe, 5lw, 5le are also each 5lpe, 51w, 5le and one of connected to a second power divider 52pe, 52pw, 52e, 52w, via l7pw, l7e, the second power parts 52pe, 52pw, 52e, 52w is also each a band-blocking filter l7pe, l7w each. They are connected to a protective and a "normal" booster amplifier Bpe, Bpw, Be, Bw, via power combiner 53pe, 53pw, 53e, 53w. 53pw, 53e, 53w connected to the multiplexers l5e, l5w, the switches 38e, 38w Finally, the power combiners 53pe and the transmitters 6e, 6w are also lare 55e, 55w.

The same applies to Figure 11, which is a combination of in Figure 8, via one of two power defenses Figure 9 and Figure 5b. Each preamplifier Ppw, Ppe, Pw, Pe is connected to switches 4le, 4lw, demultiplexers l3e, l3w, and receivers 5e, 5w as in figure 9, via a first power divider 5lpw, 5lpe, 5lw, 5le and two of four power combi - lower 6le, 6lw, 62e, 62w. The first power dividers 5lpw, 5lpe, 5lw, 5le are also each connected to a second power divider 52pe, 52pw, 52e, 52w, via a band-blocking filter l7pe, l7pw, l7e, 52pw, 52e, protective and a “normal Booster amplifiers Bpe, Bpw, Be, l7w each. The other power parts 52pe, 52w are also each connected to a Bw, via power combiner 53pe, 53pw, 53e, 53w. the power parts 53pe, 53pw, 53e, couplers 42e, 42w, multiplexers l5e, l5w, Finally, 53w are also connected to inverters and transmitters 6e, 6w, as in figure 8, via two of four power dividers 63e, 63w, 64e, 64w.

Claims (6)

10 15 20 25 30 521 135 Éfíïfíï-ífï fi fííï- 15 PATENTKRAV A communication network comprising at least two nodes (N1, N2, N3, N4, N5, N6, N7, N8), which network has two communication paths (2, 3) which transmit traffic in opposite directions and function as a bidirectional bus, which network always has a first inactive segment (S1) which does not transmit any traffic and which network is arranged to allow the first inactive segment (S1) to be made active and a second segment in particular in the case of a fault (F1) in the second the segment, the activation and deactivation being made inactive, is like logically moving the first inactive segment (S1), characterized by additional protection paths (L1, L2, L3, L4, L5, L6, L7, L8, L9, L10, L11) are arranged between the nodes (N1, N2, N3, N4, N5, N6, N7, N8) to allow the faulty segment (S1) to be bypassed and a further faulty segment (S2) on the bus rendered inactive. A communication network according to claim 1, characterized in that the protection paths (L9) are substantially parallel to the communication paths. A communication network according to claim 1, characterized in that the protection paths (L1, L2, L3, L4, L5, L6, L7, L8, L10, L11) are connected via multidirectional cross points (C1, C2, C3) to form a network between the nodes (N1, N2, N3, N4, N5, N6, N7, N8). A communication network according to any one of claims 1-3, characterized in that the nodes comprise receivers (5), transmitters (6) and means (Pw, Pe, Bw, Be) for creating an inactive segment (S1) in one of the the communication links (2, 3) connected to the node, that the nodes also comprise means (11p, 12, 14p, 16, 18e, 18w, 31, 33e, 33w, 32, 36e, 36w, 51pe, 54e, 54w, 52e, 52w, 53pe, 53pw, 55e, 55w, 61e, 61w, 62e, 62w, 63e, 63w, 64e, 64w) 51pw, to connect one or more of the protective links (L1, L2, L3, L4, L5, L6, L7 , L8, L9, L10, L11). 10 15 20 -v -H. - 1 - »w. 521 135/6 A communication network according to claim 4, characterized in that the nodes also comprise means (Pp, Bp, Ppw, Ppe, Bpw, Bpe) for creating an inactive segment (S2, S3) in the protection link or links (L1, L2, L3, L4 , L5, L6, L7, L8, L9, L10, L11). Method for error handling in a communication network comprising at least two nodes (N1, N2, N3, N4, N5, N6, N7, N8), which network has two communication paths (2,3) which transmit traffic in opposite directions and function such as a bi-directional bus, which network always has a first inactive segment that does not transmit any traffic, comprising the following steps: detecting an error (F1) in an incorrect segment (S1), when the error (F1) is not in the the first inactive segment, to inactivate the inactive segment and the faulty segment, characterized by detecting a faulty (F2) segment (S2) on the bus, in a further faulty segment, bypassing the faulty segment (S1) and inactivate the additional incorrect segment (S2).